15/100 = 15%
A value of 15% might show up as a discount on a jacket, a tip at a restaurant, or the battery left on a phone. It means the amount is a small but noticeable part of the whole.
To picture it quickly, imagine 100 equal squares and shade 15 of them. You can also think of it as a little less than one-sixth of the whole.
A common mix-up is confusing 15% with 15 percentage points when comparing two rates. For example, a rate rising from 10% to 15% goes up by 5 percentage points, not 15.
